I remember seeing those years ago. Nice idea.
I think what has happened is that quality, all-screen caging is readily available now at fair prices. So are the glass terrariums by ExoTerra and ZooMed, and these are generally priced quite well. With the above products at hand, a tank topper may not have a large demand anymore. This is my guess.
I believe you can still find them online. I was browsing online at an educational supply site that has secure, ventilated plastic boxes suitable for small reptiles and other critters, and they had a tank topper on there. It cost as much as a new screen cage.